I have a similar problem, but I'm not sure setting the yAxisMaxValue to be the same for both charts will work for me, as they have different scales:
It is necessary for the second chart to have the formatNumberScale=1 setting, but not for the first chart. The first chart will generally be less than 300 (average around 80), but the second chart could be +/- about 120000. If I set the yAxisMaxValue to 110000 for both charts, the line on the first chart becomes too small to see, as the scale is too big.
Is there a way to get the left-hand edgeline of both chart plot areas (to the right of the y-axis labels) to align?
Cheers